Monitoring saturation changes in an oil field over time, known as reservoir saturation monitoring (RSM), is a routine operation for oil companies to assess oil recovery efficiency and to identify zones for sidetrack or perforation. Reservoir saturation monitoring offers particular advantages for parts of a field that have started producing water. Currently, decisions relating to reservoir saturation monitoring involve petrophysicists, in consultation with reservoir and production engineers and service-company logging engineers. Although routine, RSM is a complex and time-consuming operation. In addition, RSM decisions are subject to human error.
Various logging technologies, from various vendors, can be available for or involved with reservoir saturation monitoring, and each logging technology has its advantages and disadvantages. For example, deep resistivity logs read more than 10 times deeper into a reservoir than shallow carbon-oxygen logs; resistivity logs are, however, water salinity dependent, unlike carbon-oxygen logs, and do not provide desirable results in a fresh or mixed water environment.
Wells having various well conditions and attributes can be the subject of reservoir saturation monitoring. For example, candidate wells for RSM can include active wet producers with different water cuts, different minimum tubing restrictions, different logging intervals, wells that have been dead or shut-in for a long time, wells that have been mothballed by pumping thousands gallons of diesel, and wells that have been massively acidized (and thus near-wellbore rock properties may have been altered). Moreover, these conditions can affect the technologies associated with reservoir saturation monitoring.
Thus, there exists a need for more reliable and efficient methods and apparatuses for the determining appropriate technologies for well saturation monitoring.